The present invention pertains to a rotary screw compressor with a lift valve mounted in the high pressure end wall of the compressor, said lift valve comprising a valve member having two rigidly connected cylindrical sections of different diameter displaceably mounted in a valve housing, said valve housing sealingly surrounding each of said sections, the section of the smaller diameter and the corresponding part of the valve housing facing the working space of the machine.
A machine of the rotary screw type in question comprises two rotors mounted in a working space, which is limited by two end walls and a barrel wall extending therebetween. The barrel wall has the shape of two intersecting cylinders, each housing one of the rotors. Each rotor is provided with helically extending lobes and grooves, being in intermesh to form chevron-shaped compression chambers. In these chambers a gaseous fluid is displaced and compressed from an inlet channel to an outlet channel. Each compression chamber during a filling phase communicates with the inlet, during a compression phase undergoes a continuous reduction in volume and during a discharge phase communicates with the outlet. Reference is made U.S. Pat. No. 4,435,139 disclosing an example of this general type of compressor.
Machines of this kind often are provided with valve means for regulating the built-in volume ratio (V.sub.i) or the capacity or for other purposes. When continuous regulation is required, usually slide valves are used, whereas at simpler regulation needs it might be sufficient to use lift valves. Such a valve is mounted in the barrel wall of the machine or in one of the end walls, normally the high pressure end wall.
In known rotary screw compressors having a lift valve in one of the end walls, the lift valves are axially directed. This, however, in some cases can cause a problem to attain space enough for the lift valve, as the end wall section also has to house bearings and seals for the shafts of the rotors. The object of the present invention therefore is to construct the valve in a rotary screw compressor of the discussed above, specified kind in such a way that said problem is overcome.